The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, a vehicle 100 includes an oxygen sensor 102 that is connected to an engine control module (ECM) 104. The oxygen sensor 102 determines an amount of oxygen in an air/fuel mixture combusted by an engine of the vehicle 100. The oxygen sensor 102 may provide a voltage output that corresponds to the oxygen level. The ECM 104 controls various engine functions based on oxygen level. For example, the ECM 104 measures voltage across a load resistor RLoad that is connected to the oxygen sensor 102 and controls the amount of fuel added to the air/fuel mixture based on the measured voltage.
The oxygen sensor 102 may not be “ready” when the vehicle 100 is initially started. For example, the oxygen sensor 102 may not provide reliable measurements when the vehicle 100 is initially started. Accordingly, the ECM 104 may initially ignore measured oxygen levels and instead use predetermined (i.e. stored) data. The ECM 104 may continue to use the predetermined data until the oxygen sensor 102 provides reliable measurements. As such, the vehicle 100 operates in an open loop mode until the oxygen sensor 102 measurements are used.
When the oxygen sensor 102 is ready, the ECM 104 uses the measured oxygen levels and the system operates in a closed loop mode. When the vehicle 100 is operated in the closed loop mode, overall engine operation may be improved. For example, the ECM 104 may adjust how much fuel is added to the air/fuel mixture more accurately based on the measured oxygen levels, decreasing vehicle emissions.
Measurements of the oxygen sensor 102 may be taken across RLoad. The oxygen sensor 102 may be modeled as a resistor R1 and a voltage source V1. Initially, when the vehicle 100 is started, R1 may be large. R1 may then decrease in resistance as the temperature of the oxygen sensor 102 increases. For example, initially the temperature of the oxygen sensor 102 may be 200° C. and R1 may measure 4 MΩ. As the temperature increases to 700° C., R1 may measure 20Ω.
While R1 changes based on temperature, V1 is determined by the oxygen level of the air/fuel mixture. For example, a voltage of 0.2 volts may correspond to an oxygen level resulting from a low air/fuel ratio, while 0.8 volts may correspond to a high air/fuel ratio. The ECM 104 measures the voltage across Rload to determine the oxygen level and thereby regulate the air/fuel mixture.
The oxygen sensor 102 may be diagnosed for faults such as open circuits. A bias voltage module 106 may be included in the system so that diagnostics may be performed. The bias voltage module 106 may include a voltage source V2 and resistor R2 in series. The voltage source V2 is a fixed voltage source. The resistor R2 of the bias voltage module 106 is fixed. For example, V2 may be 1.9 volts and R2 may be 600Ω. RLoad may also be a fixed resistor.